This invention relates to power supply systems which furnish DC current at a certain voltage to segmented electrical loads; and more particularly, it relates to such power supply systems which include a redundant current sharing power supply and which enable the various segmented loads to be turned off for repair while the remainder of the loads continue to operate.
Electrical loads, such as integrated circuits, frequently are packaged on printed circuit boards which have power and ground pins as well as multiple input/output pins for receiving and sending signals. Hundreds of these boards are often included in a single electronic system, such as a large data processing system or a large communications system. Multiple backplanes are commonly provided to hold the boards in groups of 10 to 20, and each backplane has its own power and ground buses.
One way to provide power to such a multiple backplane system is to cable the power buses of all the backplanes together, and to connect them to a set of power supplies which operate in parallel to share in furnishing the total load current. Also, a redundant supply (i.e., an extra supply) can also be included in such a system so that if any one power supply fails, the electronic system can still operate. This type of power supply system, including a redundant supply, is described in U.S. patent application Ser. No. 934,025 by J. Miller and J. Walker which is assigned to the present assignee.
However, in a multiple backplane electronic system, it is often desirable to power down the circuitry on just one backplane while the circuitry on the remaining backplanes continues to operate. For example, large data processing systems often contain multiple digital computers, each of which is housed on a different backplane. When the circuitry in one of those computers fails, it is desirable to be able to power down just the backplane of the failed computer so that its circuitry can be repaired while at the same time, the remaining computers continue to operate. However, with the above referenced power supply system, this cannot be done because there, power cannot be independently applied to and removed from the individual backplanes.
One way to solve the above problem is to not connect the power buses of the backplanes together and to provide a separate set of power supplies, such as those of the referenced power supply system, for each backplane. But in that case, a separate redundant supply would also have to be provided for each backplane; and that would substantially increase the cost of the system. For example, consider an electronic system which has three backplanes A, B, and C. Suppose further that backplane A requires three power supplies to furnish its load current; backplane B requires just one power supply to furnish its load current; and backplane C requires two power supplies to furnish its load current. In that case, a total of six power supplies is required to furnish the needed load current, but an additional three redundant supplies (one for each backplane) is required to provide redundancy. Thus, the cost of the system is increased by 50%!
Accordingly, it is a primary object of the invention to provide a power supply system in which all of the above problems are avoided.